High copper low alloy steel sheet

ABSTRACT

A high copper low alloy steel sheet made by the steps comprising preparing a molten melt producing an as-cast low alloy steel comprising by weight, between 0.02% and 0.3% carbon, between 0.10% and 1.5% manganese, between 0.01% and 0.5% silicon, between 0.002 and 0.0095% sulfur, greater than 0.01% and less than or equal to 0.15% phosphorus, less than 0.05% aluminum, more than 0.20% copper, less than 0.03% tin, and less than 0.10% nickel, and the remainder iron and impurities resulting from melting, and solidifying the molten melt into sheet less than 10 mm in thickness in a non-oxidizing atmosphere to below 1080° C. The copper content may be between 0.2% and 2.0% by weight. The high copper low alloy steel may also have a corrosion index (I) of at least 6.0 in accordance with ASTM G101 where: I=26.01 (% Cu)+3.88 (% Ni)+1.20 (% Cr)+1.49 (% Si)+17.28 (% P)−7.29 (% Cu)(% Ni)−9.10 (% Ni)(% P)−33.39 (% Cu) 2 . The high copper low alloy steel may be produced by twin roll casting, and may have thickness less than 5 mm or less than 2 mm in thickness.

RELATED APPLICATION

The present application is a continuation-in-part of application Ser.No. 10/805,831, filed Mar. 22, 2004.

BACKGROUND AND SUMMARY OF THE INVENTION

Previously high copper low-alloy steel sheet was known and was known toprovide corrosion resistance; however, such low alloy steel containingabout 0.50% or more of copper frequently exhibited “hot shortness”during hot working, so that cracks or extremely roughened surfaces,sometimes referred to as “checking,” may develop during hot deformation.See, The Making, Shaping and Treating of Steel (9^(th) edition) at page1154. Hot shortness occurs by copper separating during surface oxidationfrom the oxidizing layer to a layer adjacent the surface of the producedsheet resulting in a commercially unacceptable steel. The occurrence ofthese undesirable surface conditions could be minimized by carefulcontrol of oxidation during heating and taking care not to overheatduring hot working. Also, the addition of nickel in an amount equal toat least one-half the copper content has been known to be verybeneficial to the surface quality of steels containing copper. However,these procedures and alloying additions were expensive and caused theresulting corrosion resistant steels to be expensive. Notably, nickel isan expensive alloy addition and causes the resulting corrosion resistantsteel to be expensive.

Copper, in the concentrations used, was known to be the most potent ofall common alloying elements in improving atmospheric-corrosionresistance in carbon steels. Copper was known to be especially effectivein amounts up to about 0.35% in regular carbon steel. As noted, thesteels with about 0.50% or more copper presented the problem of hotshortness. However, these levels of copper were acceptable in slabs ofthe order of 100 mm or more, where the adverse effects of hot shortnesscould be minimized by the later hot reduction of the strip.

The tolerance for copper is reduced with the reduction in thickness ofthe slab. For a thickness of 50 mm produced in the thin slab caster, ithas been found that the copper levels should be about 0.20% or below byweight of copper, to avoid the deleterious effects of hot shortness inthe sheet. Indeed, it has been found that the levels of copper typicallyneed to be maintained below 0.10% to avoid the inhibiting impact of hotshortness on the sheet made from such thin slabs. FIGS. 1 and 2 show thedeleterious effects of hot shortness in the surface a slab of 50 mm inthickness made by a thin slab caster. This was with a steel compositionwith medium carbon and both copper and nickel additions, namely, 0.18%carbon, 0.53% manganese, 0.009% phosphorus, 0.008% sulfur, 0.025%silicon, 0.23% copper, 0.21% nickel, 0.01% tin and 0.06% chromium. Notethat as shown in FIGS. 1 and 2, even with nickel additions about thesame as copper additions hot shortness was experienced.

The problem of hot shortness also has increased the costs in making lowalloy steel using electric arc furnaces to form the molten carbon steel.Approximately 75% of the cost of making steel by electric arc furnace isthe cost of the scrap used as the starting material for charging theelectric arc furnace. Steel scrap has been traditionally separated bycopper content to less than 0.15% by weight copper, greater than orequal to 0.15% to up to 0.5% by weight copper, and above 0.5% by weight.Scrap with copper content above 0.5% copper could be mixed with scrapwith low copper levels to make an acceptable scrap, which also added tothe cost of the scrap commercially available. In any event, the scrapwhich was low copper below 0.15% by weight is the highest cost scrap,with the other two grades of scrap being of less cost. In making steelsheet by traditional commercial processes, such as by continuous thickslab or thin slab casting, only scrap with less than 0.15% copper isgenerally useful in electric arc furnaces. This adds considerably to thecost of the steel sheet produced. Scrap grades with copper content up to0.5% were useful in electric arc furnaces servicing bar mills, or atconsiderable expense by mixing with scrap of lower copper content toreduce the overall copper content of the scrap to less than 0.15%.

Applicant has found that high copper low alloy steel sheet of 10 mm inthickness and less can be produced without the addition of substantialnickel alloy by solidification and cooling in a non-oxidizing atmosphereto less than 1080° C., i.e., below the solidification temperature ofcopper. In this way, hot shortness is reduced by inhibiting oxidation ofthe sheet surface. By low alloy steel is meant a steel having between0.02% and 0.3% carbon, between 0.10% and 1.5% manganese, between 0.01%and 0.5% silicon, between 0.002 and 0.0095% sulfur, greater than 0.01%and less than or equal to 0.15% phosphorus, less than 0.05% aluminum, atleast 0.20% copper, less than 0.03% tin, and less than 0.10% nickel. Thecopper content of the high copper low alloy steel may be between 0.20%and 2.0%. We have also found that the sulfur levels are particularlyimportant with levels above 0.002% needed to promote sufficient contactbetween the molten steel and the surfaces of the caster (with increasedsulfur levels reducing chafter defects), but below 0.0095% to avoidmarked crocodile skin roughness and cracking in the surface of the caststrip. The sulfur content may be between 0.003 and 0.009%. Anon-oxidizing atmosphere is an atmosphere typically of an inert gas suchas nitrogen or argon, or a mixture thereof, that contains less thanabout 5% oxygen by weight.

The high copper low alloy steel may also have a corrosion index (I) ofat least 6.0 in accordance with ASTM G101-01 where:I=26.01 (% Cu)+3.88 (% Ni)+1.20 (% Cr)+1.49 (% Si)+17.28 (% P)−7.29 (%Cu)(% Ni)−9.10 (% Ni)(% P)−33.39 (% Cu)².

The high copper low alloy steel sheet may be made by the stepscomprising:

-   -   (a) preparing a molten melt producing an as-cast low alloy steel        comprising        -   (i) by weight, between 0.02% and 0.3% carbon, between 0.10%            and 1.5% manganese, between 0.01% and 0.5% silicon, between            0.002 and 0.0095% sulfur, greater than 0.01% and less than            or equal to 0.15% phosphorus, less than 0.05% aluminum, more            than 0.20% copper, less than 0.03% tin, and less than 0.10%            nickel;        -   (ii) the remainder iron and impurities resulting from            melting;    -   (b) solidifying and cooling the molten melt into a sheet less        than 10 mm in thickness in a non-oxidizing atmosphere to below        1080° C.

The high copper low alloy steel sheet may also be made by the stepscomprising:

-   -   (a) preparing a molten melt producing an as-cast low alloy steel        comprising        -   (i) by weight percent, between 0.02% and 0.3% carbon,            between 0.10% and 1.5% manganese, between 0.01% and 0.5%            silicon, between 0.002% and 0.0095% sulfur, greater than            0.01% and less than or equal to 0.15% phosphorus, less than            0.05% aluminum, more than 0.20% copper, less than 0.03% tin,            and less than 0.05% nickel;        -   (ii) the remainder iron and impurities resulting from            melting;    -   (b) forming the melt into a casting pool supported on casting        surfaces of a pair of cooled casting rolls having a nip        therebetween;    -   (c) counter rotating the casting rolls to form a thin cast sheet        or strip of less than 10 millimeters in thickness extending        downwardly from the nip; and    -   (d) cooling the cast strip to below 1080° C. in a non-oxidizing        atmosphere.

The thickness of the high copper low alloy steel sheet (orstrip)produced may be less than 5 mm in thickness or less than 2 mm inthickness. The copper content of the high copper low alloy steel may bebetween 0.20% and 2.0%. Aagain, non-oxidizing atmosphere is anatmosphere typically of an inert gas such as nitrogen or argon, or amixture thereof, that contains less than about 5% oxygen by weight.

Again, the high copper low alloy steel may also have a corrosion indexof at least 6.0 in accordance with ASTM G101-01 where:I=26.01 (% Cu)+3.88 (% Ni)+1.20 (% Cr)+1.49 (% Si)+17.28 (% P)−7.29 (%Cu)(% Ni)−9.10 (% Ni)(% P)−33.39 (% Cu)².

Also disclosed is a high copper low alloy steel of less than 10 mm inthickness made by a particular method. A twin roll caster may be used inmaking the high copper low alloy steel by the disclosed method asdescribed in more detail below. Again, the high copper low alloy steelstrip may be less than 5 mm in thickness or less than 2 mm in thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more fully explained, illustrativeresults of experimental work carried out to date will be described withreference to the accompanying drawings in which:

FIGS. 1 and 2 are micrographs illustrating hot shortness experienced inthe prior art with corrosion resistant low alloy steel made by thin slabcasting;

FIG. 3 is a diagrammatic side elevation view of an illustrative twinroll strip caster;

FIG. 4 is an enlarged sectional view of a portion of the illustrativecaster of FIG. 3;

FIG. 5 is a graph showing the benefits of the high copper low alloysteel of the present invention compared to prior low alloy steel withcopper additions;

FIGS. 6 and 7 are micrographs showing the surface of high copper lowalloy steel sheet of 1.7 mm in thickness made by thin strip casting,showing the inhibiting of hot shortness.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 3 and 4 illustrate a twin roll continuous strip caster which hasbeen operated in making high copper low alloy steel strip in accordancewith the present invention. The following description of the describedembodiments is in the context of continuous casting steel strip using atwin roll caster. The present invention is not limited, however, to theuse of twin roll casters and extends to other types of continuous stripcasters and other ways of making steel sheet.

FIG. 3 shows successive parts of an illustrative production line wherebysteel sheet (or strip) can be produced in accordance with a twin rollcaster. FIGS. 3 and 4 illustrate a twin roll caster denoted generally as11 which produces a cast steel strip 12 that passes in a transit path 10across a guide table 13 to a pinch roll stand 14 comprising pinch rolls14A. Immediately after exiting the pinch roll stand 14, the stripoptionally may be passed into a hot rolling mill 16 comprising a pair ofreduction rolls 16A and backing rolls 16B by which it is hot rolled toreduce its thickness. In either event, the rolled strip passes onto arun-out table 17 on which it may be cooled by convection and/or bycontact with water supplied via water jets 18 (or other suitable means)and by radiation. In any event, the rolled strip may then pass through apinch roll stand 20 comprising a pair of pinch rolls 20A and thence to acoiler 19. Final cooling (if necessary) of the strip takes place bycooling of the coil after coiling.

As shown in FIG. 4, twin roll caster 11 comprises a main machine frame21 which supports a pair of horizontally positioned casting rolls 22each having casting surfaces 22A, assembled side-by-side with a nip 27between them. Molten metal may be supplied during a casting operationfrom a ladle (not shown) to a tundish 23, through a refractory shroud 24to a distributor 25 (also called a removable tundish) and thence througha metal delivery nozzle 26 generally above the nip 27 between thecasting rolls 22. Molten metal thus delivered to the nip 27 forms acasting pool 30 above the nip 27 supported on the casting roll surfaces22A. This casting pool is confined at the ends of the rolls typically bya pair of side closure dams or plates 28, which may be positionedadjacent the ends of the rolls by a pair of thrusters (not shown)comprising hydraulic cylinder units (or other suitable means) connectedto the side plate holders. The upper surface of casting pool 30(generally referred to as the “meniscus” level) may rise above the lowerend of the delivery nozzle 26 so that the lower end of the deliverynozzle is immersed within this casting pool.

Casting rolls 22 are internally cooled by water or other suitablecoolant so that shells of steel solidify on the moving casting surfaces22A of the rolls 22 during rotation of the rolls. The solidified shellsare then brought together at the nip 27 between the casting rolls toproduce the cast strip 12, which is delivered downwardly from the nip.

As illustrated, frame 21 supports a casting roll carriage which ishorizontally movable between an assembly station and a casting station.Casting rolls 22 are counter-rotated through drive shafts (not shown)driven by an electric motor and transmission. Rolls 22 have copperperipheral walls formed with a series of longitudinally extending andcircumferentially spaced cooling passages supplied with coolant. Therolls may typically be about 500 mm in diameter and generally up toabout 2000 mm long, in order to produce strip product of about 2000 mmwide.

Removable tundish 25 is of conventional construction. It is formed as adish made of a refractory material such as for example magnesium oxide(MgO). One side of the tundish receives molten metal from the ladle andis provided with an overflow spout and an emergency plug as shown inFIG. 4.

Delivery nozzle 26 is formed as an elongate body made of a refractorymaterial such as for example alumina graphite. Its lower part is taperedso as to converge inwardly and downwardly above the nip between castingrolls 22. Nozzle 26 may have a series of horizontally spaced generallyvertically extending flow passages to produce a suitably low velocitydischarge of molten metal throughout the width of the casting rolls 22and to deliver the molten metal onto the roll surfaces 22A of the rolls22 where initial solidification occurs. Alternatively, the nozzle 26 mayhave a single continuous slot outlet to deliver a low velocity curtainof molten metal directly above the nip between the rolls. Here again,the nozzle may be immersed in the molten metal pool 30.

The casting pool 30 is confined at the ends of the rolls by a pair ofside closure plates 28 which are adjacent to and held against steppedends of the rolls 22 when the roll carriage is at the casting station.Side closure plates 28 are illustratively made of a strong refractorymaterial, for example boron nitride, and have scalloped side edges tomatch the curvature of the stepped ends of the rolls 22. The side plates28 can be mounted in plate holders which are movable at the castingstation by actuation of a pair of hydraulic cylinder units (or othersuitable means) to bring the side plates into engagement with thestepped ends of the casting rolls 22 to form end closures for thecasting pool 30 of metal supported on the casting roll surfaces 22Aduring a casting operation.

The twin roll caster may be of the kind illustrated and described insome detail in, for example, U.S. Pat. Nos. 5,184,668; 5,277,243;5,488,988; and/or 5,934,359; U.S. patent application Ser. No.10/436,336; and International Patent Application PCT/AU93/00593, thedisclosures of which are incorporated herein by reference. Reference maybe made to those patents for appropriate constructional details but suchdetails form no part of the present invention.

To illustrate, high copper low alloy steel sheet was made by twin rollcaster into thin cast steel strip of 1.7 mm in thickness. The steelstrip had the following chemical composition: 0.048% carbon, 0.636%manganese, 0.117% phosphorus, 0.005% sulfur, 0.252% silicon, 0.261%copper, 0.034% nickel, 0.027% chromium, 0.015% molybdenum, 0.006% tin,0.001% aluminium, 0.001% titanium, 0.001% zinc, 0.0072% nitrogen andother impurities normally found in steel scrap. The steel was alsotested and not found to have any measurable amounts of vanadium, lead,calcium or boron. This steel was designated heat #232613 (trial #1), andwas made into four coils (i.e., numbers 1,2,3 and 4) which were tested.

A second high copper low-alloy steel sheet was made by twin-roll casterinto thin cast strip of 1.7 mm in thickness. The steel strip had thefollowing chemical composition: 0.049% carbon, 0.554% manganese, 0.043%phosphorus, 0.009% sulfur, 0.227% silicon, 0.417% copper, 0.030% nickel,0.067% chromium, 0.011% molybdenum, 0.005% tin, 0.001% aluminium, 0.001%lead, 0.001% titanium, 0.001% zinc, 0.0065% nitrogen and otherimpurities normally found in steel scrap. The composition was alsotested for vanadium, niobium, calcium and boron and none were measured.This steel was designated heat #137162 (trial #2), and was made intofour coils (i.e., numbers 1,2,3 and 5) which were tested. There was nota roll #4 tested, because it was a pup.

The coils from Trials 1 and 2 were tested and the results are shown inTable 1 below. Tensile Thickness Yield Strength Total Elongation Heat#-Coil # (mm) (psi) (psi) (percent) 232613-01 1.7 48,800 74,600 22.2232613-02 1.7 43,500 76,900 21.2 232613-03 1.7 46,000 72,700 22.2232613-04 1.7 47,200 76,400 21.7 137162-01 1.7 48,100 67,500 23.2137162-02 1.7 52,800 71,800 18.2 137162-03 1.7 57,000 73,200 16.2137162-05 1.7 55,600 73,400 19.7

These data compare well for initial trials with ASTM 606 which specifiesa minimum yield of 50,000 psi, a minimum tensile strength of 70,000 psiand a minimum elongation of 22%. The elongation property of the steelstrip in these trials evidences the reduction, if not elimination, ofhot shortness since hot shortness typically resulted in a totalelongation in prior steel strip of below 10%.

These data also illustrate the operation of the invention with differentsulfur levels within the range from 0.002%, needed to promote sufficientcontact between the molten steel and the surface of the casting rolls,to at or below 0.0095% to avoid severe crocodile skin roughness andcracking in the surface of the cast strip. Specifically, the sulfurcontent in the first steel strip was 0.005% and the sulfur content inthe second steel strip was 0.009%. As previously noted, the sulfur levelmay be between 0.003 and 0.009%.

FIG. 5 shows the dramatic improvement in inhibiting hot shortness withthe high copper low alloy steel sheet of the present invention. Thesolid line illustrates the tolerance of prior art sheet to hot shortnessas a function of percent copper from available data. The dotted line isan extension of the solid line showing the projected levels of copperthat can be tolerated without hot shortness in sheet below 10 mm inthickness As can be seen from FIG. 5, those copper levels are below0.15% and closer to and below 0.1%. By contrast, the levels of copperthat can be tolerated without substantial hot shortness in the highcopper low alloy steel sheet of the present invention under 10 mm inthickness is more than 0.2%, and 0.4% and higher, with a cast strip of1.7 mm thickness. Indeed, high copper low alloy steel as high as 1.5%copper has been cast without hot shortness at a thickness of 1.9 mm.

FIGS. 6 and 7 are micrographs of the surfaces of the high copper lowalloy sheet or strip showing an absence of hot shortness. The benefitsin inhibiting hot shortness are most evident by comparing FIGS. 6 and 7with FIGS. 1 and 2 above. The high copper low alloy steel also may havea the corrosion index (I) of at least 6.0 where:I=26.01 (% Cu)+3.88 (% Ni)+1.20 (% Cr)+1.49 (% Si)+17.28 (% P)−7.29 (%Cu)(% Ni)−9.10 (% Ni)(% P)−33.39 (% Cu)².

Although the invention has been described in detail with reference tocertain embodiments, it should be understood that the invention is notlimited to the disclosed embodiments. Rather, the present inventioncovers variations, modifications and equivalent structures that existwithin the scope and spirit of the invention and such are desired to beprotected.

1. A high copper low alloy steel sheet made by the steps comprising: (a)preparing a molten melt producing an as-cast low alloy steel comprising(i) by weight, between 0.02% and 0.3% carbon, between 0.10% and 1.5%manganese, between 0.01% and 0.5% silicon, between 0.002 and 0.0095%sulfur, greater than 0.01% and less than or equal to 0.15% phosphorus,less than 0.05% aluminum, more than 0.20% copper, less than 0.03% tin,and less than 0.10% nickel; (ii) the remainder iron and impuritiesresulting from melting; (b) solidifying and cooling the molten melt intoa sheet less than 10 mm in thickness in a non-oxidizing atmosphere tobelow 1080° C.
 2. The high copper low alloy steel sheet as claimed inclaim 1 wherein the corrosion index (I) is at least 6.0 where:I=26.01 (% Cu)+3.88 (% Ni)+1.20 (% Cr)+1.49 (% Si)+17.28 (% P)−7.29 (%Cu)(% Ni)−9.10 (% Ni)(% P)−33.39 (% Cu)².
 3. The high copper low alloysteel sheet as claimed in claim 1 wherein the total of the % by weightof copper is between 0.2 and 2.0.
 4. The high copper low alloy steelsheet as claimed in claim 1 wherein the thickness of the sheet is lessthan 5 mm in thickness.
 5. The high copper low alloy steel sheet asclaimed in claim 1 wherein the thickness of the sheet is less than 2 mmin thickness.
 6. The high copper low alloy steel sheet as claimed inclaim 1 wherein the % by weight of sulfur is between 0.003 and 0.009. 7.A high copper low alloy steel sheet made by the steps comprising: (a)preparing a molten melt producing an as-cast low alloy steel comprising(i) by weight, between 0.02% and 0.3% carbon, between 0.10% and 1.5%manganese, between 0.01% and 0.5% silicon, between 0.002 and 0.0095%sulfur, greater than 0.01% and less than or equal to 0.15% phosphorus,less than 0.05% aluminum, more than 0.20% copper, less than 0.03% tin,and less than 0.10% nickel; (ii) The remainder iron and impuritiesresulting from melting; (b) forming the melt into a casting poolsupported on casting surfaces of a pair of cooled casting rolls having anip therebetween; (c) counter rotating the casting rolls to form a thincast sheet of less than 10 mm in thickness extending downwardly from thenip; and (d) cooling the cast sheet to below 1080° C. in a non-oxidizingatmosphere.
 8. The high copper low alloy steel sheet as claimed in claim7 wherein the corrosion index (I) is at least 6.0 where:I=26.01 (% Cu)+3.88 (% Ni)+1.20 (% Cr)+1.49 (% Si)+17.28 (% P)−7.29 (%Cu)(% Ni)−9.10 (% Ni)(% P)−33.39 (% Cu)².
 9. The high copper low alloysteel sheet as claimed in claim 7 wherein the total of the percent byweight of copper is between 0.2 and 2.0.
 10. The high copper low alloysteel sheet as claimed in claim 7 wherein the thickness of the thin castsheet is less than 5 mm in thickness.
 11. The high copper low alloysteel sheet as claimed in claim 7 wherein the thickness of the thin castsheet is less than 2 mm in thickness.
 12. The high copper low alloysteel sheet as claimed in claim 7 wherein the % by weight of sulfur isbetween 0.003 and 0.009.
 13. A method of making a high copper low alloysteel sheet comprising the steps of: (a) preparing a molten meltproducing an as-cast low alloy steel comprising (i) by weight, between0.02% and 0.3% carbon, between 0.10% and 1.5% manganese, between 0.01%and 0.5% silicon, between 0.002 and 0.0095% sulfur, greater than 0.01%and less than or equal to 0.15% phosphorus, less than 0.05% aluminum,more than 0.20% copper, less than 0.03% tin, and less than 0.10% nickel;(ii) the remainder iron and impurities resulting from melting; (b)solidifying the molten melt into sheet less than 10 mm in thickness in anon-oxidizing atmosphere to below 1080° C.
 14. The method of making ahigh copper low alloy steel sheet as claimed in claim 13 wherein thecorrosion index (I) is at least 6.0 where:I=26.01 (% Cu)+3.88 (% Ni)+1.20 (% Cr)+1.49 (% Si)+17.28 (% P)−7.29 (%Cu)(% Ni)−9.10 (% Ni)(% P)−33.39 (% Cu)².
 15. The method of making ahigh copper low alloy steel sheet as claimed in claim 13 wherein thetotal of the percent by weight of copper is between 0.2 and 2.0.
 16. Themethod of making a high copper low alloy steel sheet as claimed in claim13 wherein the thickness of the thin cast strip is less than 5 mm inthickness.
 17. The method of making a high copper low alloy steel sheetas claimed in claim 13 wherein the thickness of the thin cast strip isless than 2 mm in thickness.
 18. The method of making high copper lowalloy steel sheet as claimed in claim 13 wherein the % by weight ofsulfur is between 0.003 and 0.009.
 19. A method of making a high copperlow alloy steel sheet comprising the steps of: (a) preparing a moltenmelt producing an as-cast low alloy steel comprising (i) by weight,between 0.02% and 0.3% carbon, between 0.10% and 1.5% manganese, between0.01% and 0.5% silicon, between 0.002 and 0.0095% sulfur, greater than0.01% and less than or equal to 0.15% phosphorus, less than 0.05%aluminum, more than 0.20% copper, less than 0.03% tin, and less than0.10% nickel; (ii) the remainder iron and impurities resulting frommelting; (b) forming the melt into a casting pool supported on castingsurfaces of a pair of cooled casting rolls having a nip therebetween;(c) counter rotating the casting rolls to form a thin cast sheet of lessthan 10 mm in thickness extending downwardly from the nip; (d) coolingthe cast sheet to below 1080° C. in a non-oxidizing atmosphere.
 20. Themethod of making a high copper low alloy steel sheet as claimed in claim19 wherein the corrosion index (I) is at least 6.0 where:I=26.01 (% Cu)+3.88 (% Ni)+1.20 (% Cr)+1.49 (% Si)+17.28 (% P)−7.29 (%Cu)(% Ni)−9.10 (% Ni)(% P)−33.39 (% Cu)².
 21. The method of making ahigh copper low alloy steel sheet as claimed in claim 19 wherein thetotal of the percent by weight of copper is between 0.2 and 2.0.
 22. Themethod of making a high copper low alloy steel sheet as claimed in claim19 wherein the thickness of the thin cast strip is less than 5 mm inthickness. 23 The method of making a high copper low alloy steel sheetas claimed in claim 19 wherein the thickness of the thin cast strip isless than 2 mm in thickness.
 24. The method of making high copper lowalloy steel sheet as claimed in claim 19 wherein the % by weight ofsulfur is between 0.003 and 0.009.